Membrane extraction with a sorbent interface for headspace monitoring of aqueous samples using a cap sampling device.

A cap-shaped device was employed for headspace sampling. This sampling device coupled to membrane extraction with a sorbent interface (MESI) is intended to perform on-site and on-line aqueous sample monitoring. A laboratory sampling testwas performed both at the water surface and under water, and it showed some advantages in underwater monitoring. A group of volatile organic compounds (VOCs), varying in PDMS/gas and gas/water distribution constants, benzene, toluene, ethylbenzene, o-xylene, and trichloroethylene (TCE), was used for the sampling study. Magnetic stirring of the sample and circulation of the headspace air with a microfan were used for the enhancement of mass transfer between sample matrix and membrane to obtain higher extraction rate and efficiency. The agitation approaches were investigated individually and compared. The results showed that simultaneous agitation in water and air could greatly improve the extraction efficiency. Good linearity and precision and low detection limits were obtained for water-surface monitoring. The study demonstrated that Cap-MESI is a useful tool for field headspace monitoring of volatile organic compounds.